In the printing industry there is a need to have a quick and cheap method for proofing the color separation records prior to the preparation of the elements useful in a long-term and expensive printing process. Many techniques have been developed for providing pre-press color proofing systems to meet the need of the industry. One such color proofing system is the lamination of tacky photopolymer elements to a support such as paper and imaging of the tacky images by means of colorants. This system is positive-working. Another known color proofing system involves the use of photopolymer elements having sandwiched between a support and a removable cover sheet a nontonable photopolymerizable layer and a tonable, tacky elastomer coating composition. This system is negative-working. Other nonphotopolymerizable color proofing systems are known. Each of these pre-press color proofing systems closely matches the press sheet. The images produced in this manner generally are "nonplanar" and have a somewhat relief appearance. The image thus may appear slightly distorted or unsharp due to light diffraction from the nonplanar image. This distortion appears similar to a three-dimensional affect when viewed at a slight angle from the perpendicular. Additionally, these systems usually have a final layer of supported photopolymer applied to the multicolored proof which first serves to transparentize the toned image. The final layer is generally given an overall exposure to actinic radiation to harden the layer and serve as a protective shield for subsequent handling. The support for this final layer may or may not be removed at this point. The composite element so produced, even after removal of the protective support, will have a glossy appearance, which is sometimes objectionable because the printed page being proofed is not always glossy in nature. Desired matte finishes have been difficult to achieve. Sprays have been used containing delustering agents but are messy, involve hazardous, flammable sprays, often do not cover the layer properly, yield a poor matte finish, and the solvents may attack the image-forming layer.
The application of dry particulate matter to the upper photopolymer layer of a multicolor proof also has not been satisfactory. The particulate material is generally applied to a tacky photopolymer layer, and the layer is subsequently exposed by conventional methods, i.e., in a vacuum frame. Oil-absorptive particles have been applied to tacky photopolymer surfaces without need for an overall exposure step. Generally, these oil absorptive particles have an average diameter of about 1000 nm or more. Since particles of this size can sometimes cause a very high degree of matte finish, this can lead to some loss in image detail when employed over a nonplanar image. Application of smaller particles (e.g., below 500 nm average particle size, the colloidal region) is complicated by the fact that the smaller particles tend to agglomerate during the toning procedure and thus produce the same effects noted above. It is known to apply colloidal particles (e.g., colloidal silica) by coating a binder containing mixture directly over a planar imaged surface, for example. It is not possible, however, to achieve high loadings of colloidal silica by this method and the degree of matte and image quality may suffer.
It is desirable that an adherent matte finish be provided on the nonplanar surface of a multicolor proof surprint by a quick and easy method. Such process should eliminate any three-dimensional effects of the multilayer colored proof that may be present (improve image quality), and provide a hard, nonblocking surface to which other materials, e.g., paper, do not adhere.